Prim's Implementation

#include <bits/stdc++.h>
#define maxm 3001
#define pii pair<int, int>
#define vii vector<pii>
#define pb push_back
#define mp make_pair

using namespace std;

int n, m, x, y, r, start, cost;
vector<int> vis(maxm);
vector<pii> g[maxm];

// Complete the prims function below.
void prims() {
    priority_queue<pii, vii, greater<pii> > pq;
    pq.push(mp(0, start));
    while(!pq.empty()){
        int x = pq.top().second;
        int c = pq.top().first;
        pq.pop();
        if(vis[x])
            continue;
        vis[x] = 1;
        cost += c;
        for(int i=0; i<g[x].size(); ++i)
            if(!vis[g[x][i].second])
                pq.push(g[x][i]);
    }
    cout<<cost;
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin>>n>>m;
    for(int i=0; i<m; ++i){
        cin>>x>>y>>r;
        g[x].pb(mp(r, y));
        g[y].pb(mp(r, x));
    }
    cin>>start;
    prims();
    return 0;
}